Faculty Bibliography

PURPOSE/OBJECTIVE:To test the effectiveness of a bioptic form of a peripheral vision-enhancement lens in patients with retinitis pigmentosa (RP), choroideremia, and Usher's syndrome Type II. METHODS:Fifteen patients with peripheral visual field loss were trained in the use of the amorphic lenses for driving and other everyday activities for a 3-month period. A cross-over study design was used, where one group of eight patients received training during the first 3 months of the 6-month study, and another group of seven patients received training during the second 3 months. All patients were administered a battery of clinical, psychophysical, functional, mobility, and driving assessment tests at the beginning of the study, at 3 months, and at 6 months. The assessment tests were coded according to the primary visual skill involved in the task. These visual skills included: recognition, peripheral detection, scanning, tracking, visual memory, and mobility. RESULTS:After training, the patients showed improvement in all visual skills categories on the assessment tests, with overall improvement of 37%. There was no significant difference in the levels of improvement between the two groups. Those with smaller visual field extents showed significantly greater improvement on peripheral detection and scanning tasks. Those patients trained during the first 3 months of the study maintained their skills when tested at the 6-month point. CONCLUSION/CONCLUSIONS:Patients with peripheral vision loss may benefit from a rehabilitation program which combines low vision training with amorphic lenses in a bioptic configuration.

PURPOSE: To assess the feasibility of obtaining reliable multifocal rod electroretinograms (ERGS) and to compare them to full-field ERGs. METHODS: Multifocal rod ERGs were recorded using a stimulus array of 61 hexagons. The minimum number of dark, blank frames between flashes was varied from 0 (a minimum of 13.3 msec between flashes) to 21 (a minimum of 293 msec between flashes). Full-field ERGs were obtained using trains of flashes designed to simulate the multifocal sequences. Flashes were blue (W47B), except in a few cases in which red (W26) was used to check for cone intrusion. Flash intensities varied from -1 to 1.7 log scot td-s. RESULTS: Dark-adapted, multifocal ERGs to blue flashes had a small, early component followed by a larger, late component. The early component showed little change in amplitude with increasing intensity. Comparisons with the full-field ERGs indicated that the early component was the focal response. The larger, late component was the response to stray light, and it can be suppressed with the addition of a surround. The focal response was from a relatively circumscribed retinal region. This is shown by comparing the multifocal rod responses from a patient with retinitis pigmentosa to her behaviorally measured rod visual field. CONCLUSIONS: By choosing conditions (namely, flashes of moderate intensity with a surround) to minimize the effects of stray light, multifocal rod ERGs can be recorded with sufficient localization to be clinically useful. However, the signal-to-noise ratio of these multifocal rod ERGs was poorer than for multifocal cone responses for comparable recording periods because of the need for blank frames and the slower recovery of the rods to successive presentations

To assess local retinal function in patients with retinitis pigmentosa (RP), multi-focal ERGs and local thresholds (static visual fields) were obtained on eight RP patients with visual acuities of 20/25 or better. All eight patients showed multi-focal responses with normal timing within the central 5 deg. However, there were few responses with normal timing in the areas outside the central 7.5 deg, except in the case of the only patient with a 30 Hz full-field response with normal timing. Since full-field ERGs are dominated by responses from the periphery, this finding supplies a foundation for the commonly observed delays in the full-field cone ERGs of patients with RP. With respect to amplitude, only two patients showed multi-focal responses with near normal amplitudes anywhere in the field. The loss of amplitude at any point was not a good predictor of visual sensitivity in the Humphrey visual field. On the other hand, all areas with normal timing had near normal sensitivity. Timing changes appear to be an early indication of local retinal damage to the cone system. Nearly all areas with sensitivity losses greater than 0.5 log unit, and some areas with near normal sensitivity, showed significantly delayed multi-focal ERGs. Finally areas with extreme sensitivity loss show multi-focal responses with a wide range of amplitudes and implicit times across patients, suggesting different mechanisms of disease action in different patients

PURPOSE: To determine whether the rod and cone photoreceptors are affected in patients with diabetic retinopathy. METHODS: Twelve patients with diabetes and varying levels of retinopathy and nine age-similar control observers participated in this study. Two-color (500 versus 650 nm) dark-adapted thresholds were measured as a function of retinal eccentricity. Full-field flash electroretinograms were obtained using brief, high-intensity flashes. Dark-adapted rod-isolated (Wratten 47B filter) and light-adapted cone-isolated (Wratten 26 filter) electroretinographic responses were measured as a function of flash intensity. The a-wave data were fitted with a model based on photopigment transduction to obtain values for the parameters of Rmax (the maximal response) and log S (sensitivity). Standard clinical 30-Hz flicker electroretinographic responses were also measured. RESULTS: Psychophysically measured dark-adapted thresholds were elevated primarily at eccentricities of 5 degrees and 10 degrees from the fovea. Analysis of rod and cone a-wave data showed that Rmax was normal in most of the patients, but log S was reduced. Analysis of b-wave and oscillatory potential parameters showed rod and cone postreceptoral abnormalities, including changes in the rod-isolated semisaturation constant (log k), cone-mediated 30-Hz flicker, and cone-isolated oscillatory potentials. The electrophysiological results were not significantly correlated with blood glucose or glycosylated hemoglobin level. CONCLUSIONS: The results provide evidence for rod and cone receptoral and postreceptoral deficits in patients with diabetic retinopathy. The photoreceptor changes are primarily in the log S (sensitivity) parameter and are attributed to transduction abnormalities

The multi-input technique of Sutter and Tran (1992) yields multiple focal ERGs. The purpose here was to compare the components of this multifocal ERG to the components of the standard, full-field ERG. To record multifocal ERGs, an array of 103 hexagons was displayed on a monitor. Full-field (Ganzfeld) ERGs were elicited by flashes presented upon steady background fields. The latencies of two prominent subcomponents of the full-field ERG were altered by varying the intensity of the incremental flash or the intensity of the background field. By showing that similar manipulations of the multi-input parameters produce similar changes in latency, we were able to relate the components of the multifocal ERG to the components of the full-field ERG. The biphasic responses of the multifocal ERG appear to be generated by the same cells generating the a-wave and positive peaks of the full-field cone ERG

The purpose of this study was to determine the extent of peripheral visual deficits in patients with early age-related macular degeneration (ARMD) using electrophysiological and psychophysical techniques. Dark-adaptation curves, electro-oculograms (EOGs), and electroretinograms (ERGs) were obtained from patients with early ARMD and from normally sighted control subjects. The control subjects' data were used to calculate age-dependent 95% confidence intervals for each measure of visual function. For the control subjects, performance on all our measures of visual function decreased with age. For the patients with early ARMD, the cone system absolute thresholds, EOG ratios, and cone-dominated ERG amplitudes and implicit times were within the range of normal age-related changes. Rod system absolute thresholds, cone-rod break times, and rod-dominated electroretinographic measures were abnormal in some patients. These results suggest that when the effects of aging are taken into account, some patients classified as early ARMD may not show significant changes in peripheral retinal function with standard clinical tests